This invention relates to continuous business forms assemblies and, more specifically, to multiple-ply continuous business forms assemblies.
Prior art of possible relevance includes U.S. Letters Pat. No. 2,907,585 to Sornberger issued Oct. 6, 1959.
"Tenting" has long been a vexatious problem in the manufacture of multiple-ply, continuous business forms assemblies. Most typically, such assemblies are zig-zag folded in a stack at the end of the manufacturing process along transverse lines of weakening defining the individual forms in the assembly. The phenomena of tenting is so named, because when the stack is unfolded, at each fold line, a peaked structure will appear at the margin of the assembly where the various plies are positively secured together, as by glue, which structure somewhat crudely resembles a tent. A graphic illustration of such a "tent" appears in the drawings of the above-identified Sornberger patent.
Tents occur because the various plies of the assembly move longitudinally relative to each other at the time they are initially folded into the zig-zag stack for any of a variety of reasons and are due to the fact that while the distance between the transverse lines of weakening on each ply is the same, the outermost ply at each fold lies in a path having a greater length about the fold than the path in which an innermost ply resides. This difference in length is analogous to the difference in length about a race track between inner and outermost lanes thereon.
Typically, during manufacturing, the plies are secured together by glue which ultimately, positively holds the plies together. However, at the time of folding the assembly into the zig-zag stack, the glue will not have completely set up, allowing the relative movement causing the tent. Subsequently, the glue will set up, permanently incorporating the tent in the assembly.
Tents interfere with subsequent processing as, for example, printing on the forms in high speed equipment, such as tabulators, computer printers, or the like and may, in fact, cause such equipment to stop.
Tenting is aggravated by the number of plies in the assembly. Generally, through good manufacturing techniques, assemblies having four to six plies can be manufactured without tenting so extreme as to disrupt subsequent processing operations. However, when it is attempted to increase the number of plies over and above that amount, the tenting becomes so pronounced that commercially acceptable forms cannot be manufactured.
Over the years, the prior art has tried a number of approaches to eliminate or minimize the tenting problem. The structure disclosed by Sornberger is indicative of one approach. However, it will be appreciated merely from a cursory review of the Sornberger patent that extremely complicated cutting operations and gluing operations are required.
Theoretically, tenting could be eliminated in forms wherein so-called "cold" glues are employed if the assembly line was such as to allow complete drying of such glues prior to folding of the forms. As a practical matter, for most cold glues used in the business forms industry today, and at manufacturing speeds typically used, a drying area in an assembly line following a collator whereat the plies are assembled together would have to be so long as to be totally impractical.
It has also been proposed that faster drying or so-called "hot" glues be employed. This approach, while used to some extent, is not totally satisfactory for the reason that most such hot glues dry to a greater thickness the the cold glues, with the result that the forms of the resulting assembly are considerably thicker than might be desired in the glued marginal areas and are quite stiff and thus difficult to handle.
Thus, there is a real need for a simple, but effective, means for eliminating or minimizing tenting to eliminate difficulties in subsequent processing and/or the manufacture of multiple-ply, continuous business forms assemblies having a greater number of plies than can be manufactured according to present-day techniques.